Should getUserInfo() be under IdentityProvider?

[npm1]

Per #470 review, it is awkward to have getUserInfo() hang off of IdentityProvider. However, we currently do not really have any better ideas. While we are for now keeping it there, filing this issue to keep this open for the next few months, while it is still easy to move it around, in case we find a better home for it.

[samuelgoto]

The other option we considered was hanging it on IdentityCredential as a static method, but (a) there are more methods that we'd need to find a better home to and (b) it may not fit well with this design too.

There are a few moving parts here (example), but I agree that IdentityProvider.getUserInfo() is awkward.

We are committed to moving this to a better place if we can find one while FedCM is still in its early days of adoption (say, in the next 6-12 months it should be easy to move it to another object if we find one).